5-HT3 receptor-independent inhibition of the depolarization-induced 86Rb efflux from human neuroblastoma cells, TE671, by ondansetron

Ondansetron-associated hypokalemia in a 2-year-old with pre-B-cell ALL

Ondansetron is a commonly used medication in the treatment of nausea and vomiting arising from many etiologies, including chemotherapy. Although it is a highly safe drug, ondansetron use has been associated, rarely, with hypokalemia. However, it is unknown whether hypokalemia is due to the medication itself or to an underlying potassium disturbance caused by prior metabolic derangements, including vomiting. We relate a patient who presents with hypokalemia of unknown etiology, with evidence suggesting a possible relationship to ondansetron. We also present a proposed mechanism for this phenomenon.

Conformationally restrained carbazolone-containing α,γ-diketo acids as inhibitors of HIV integrase

Since alpha,gamma-diketo acid (DKA) compounds were identified as potent and selective inhibitors for HIV integrase, numerous structural modification studies have been carried out to search for a clinical candidate as a supplement for the highly active antiretroviral therapy regimen. Due to the lack of structural information on inhibitor-integrase interactions, a comprehensive structure-activity relationship study is necessary. Most of the reported modification studies on the key alpha,gamma-diketo acid pharmacophore focused on substituting the carboxylate moiety with its bioisosteres or other electron-pair bearing heterocycles. We were interested in studying the conformation and geometry of the central diketo moiety. A series of carbazolone-containing alpha,gamma-diketo acids were designed and synthesized by applying conformational restraint onto the open-chain form of the diketo acid. These compounds showed anti-integrase activity in the low micromolar range, and integrase assay results indicated that the geometry of the diketo acid moiety is crucial to potency. Carbazol-1-one containing DKA analogs (7-8) showed a 2- to 3-fold increase in activity compared with those of carbazol-4-one containing DKA analogs (5 and 6). Alkylation of carbazol-4-one DKA nitrogen (6a-c) led to a loss of activity, suggesting this nitrogen atom may directly interact with the active site of integrase. The halogens (7b-d) and para-fluorobenzyl substituents (8a-d) on carbazol-1-one ring had little effect on potency.

The 5-HT3 receptor antagonist tropisetron inhibits T cell activation by targeting the calcineurin pathway

Tropisetron, an antagonist of serotonin type 3 receptor, has been investigated in chronic inflammatory joint process. Since T cells play a key role in the onset of several inflammatory diseases, we have evaluated the immunosuppressive activity of tropisetron in human T cells, discovering that this compound is a potent inhibitor of early and late events in TCR-mediated T cell activation. Moreover, we found that tropisetron specifically inhibited both IL-2 gene transcription and IL-2 synthesis in stimulated T cells. To further characterize the inhibitory mechanisms of tropisetron at the transcriptional level, we examined the DNA binding and transcriptional activities of NF-(kappa)B, NFAT and AP-1 transcription factors in Jurkat T cells. We found that tropisetron inhibited both the binding to DNA and the transcriptional activity of NFAT and AP-1. We also observed that tropisetron is a potent inhibitor of PMA plus ionomycin-induced NF-(kappa)B activation but in contrast TNF(alpha)-mediated NF-(kappa)B activation was not affected by this antagonist. Finally, overexpression of a constitutively active form of calcineurin indicated that this phosphatase may represent one of the main targets for the inhibitory activity of tropisetron. These findings provide new mechanistic insights into the anti-inflammatory activities of tropisetron, which are probably independent of serotonin receptor signalling and highlight their potential to design novel therapeutic strategies to manage inflammatory diseases.

Serotoninergic modulation of cell volume response to estramustine: an image-analysis study on perifused individual glioma cells

A technique of microscopy with computerised detection of early morphological changes during continuous perifusion was used to monitor the geometry changes of cultured glioma cells (MG-251) when exposed to 40 mg/L estramustine phosphate (EMP) alone or in combination with granisetron (0.1 mumol/L), ondansetron (0.1 mumol/L), or serotonin (1 mumol/L). When the cells were exposed to EMP, cell volume measured as projected cell area (PCA) rapidly increased. Serotonin and ondansetron, but not granisetron, prevented the acute EMP response (PCA). Serotonin, but none of the 5-HT3 receptor antagonists, protected against the cytotoxicity of EMP to the glioma cells as measured by a fluorometric microculture assay. Our results demonstrate hitherto unknown differences between selective 5-HT3 receptor antagonist on the cellular response to EMP and shows the necessity to study the receptor antagonists from viewpoint of interference with the antitumour drug effects on malignant cells. The perifusion technique could be used to study the effects of serotoninergic agonists and antagonists on cell volume regulation of cells exposed to anticancer drugs.

Level of punishment determines anticonflict activity of ondansetron in pigeons: comparison with buspirone and diazepam

The anticonflict effect of the selective 5-HT3 receptor antagonist, ondansetron, was investigated employing an operant conflict task in pigeons. Behavior (key pecking) was stimulated by food presentation. A fixed-interval program of alternated punished (electrical shocks) and unpunished responding was employed. The effects of drugs were evaluated at two levels punishment intensity; i.e., baseline responding during the punished interval was 5% (higher punishment) or 10% (lower punishment) of the unpunished responding rate. Ondansetron released responding suppressed by punishment only when pigeons were working at the lower levels of punishment. Under these conditions, ondansetron (100 microg/kg, i.v.), increased key pecking by 119% above control and vehicle values, and doubled the number of shocks received by the pigeons during the punished intervals. Similarly to ondansetron, the anticonflict effects of buspirone (0.3 and 1 mg/kg) and diazepam (1 and 1.5 mg/kg) were strongly dependent on the intensity of the punishing stimulus. When punished responding was suppressed to 5% of unpunished responding by applying shocks of higher intensity, diazepam and buspirone had negligible anticonflict action. However, at lower levels of punishment, diazepam and buspirone produced much greater anticonflict effects than ondansetron (p < 0.001). These results indicate that ondansetron exhibits a modest effect in releasing behaviors suppressed by punishment (anxiolytic-like action), which was highly dependent on the intensity of punishment applied. It is proposed that the anxiogenic response to punishment is less sensitive to 5-HT3 antagonists than the behavior induced by aversive, unpunished situations, where 5-HT3 antagonists have shown comparable efficacy to benzodiazepines.

Differential interaction between 5-HT3 receptors and GABAergic neurons inhibiting acetylcholine release in rat entorhinal cortex slices

The 5-HT3 receptor antagonists, ondansetron, MDL 72222 and granisetron (0.01-1 microM), produced a concentration-dependent increase of K+-evoked [3H]ACh efflux in slices from rat entorhinal cortex preloaded with [3H]choline. Bicuculline and flumazenil, antagonists at different sites of the GABAA receptor, also enhanced [3H]ACh efflux. While the ACh releasing effect of ondansetron was markedly potentiated, in a TTX-sensitive manner, by bicuculline, the effects of MDL 72222 and granisetron were not significantly modified. A qualitatively identical interaction was found by using flumazenil, a GABAA antagonist at the benzodiazepine recognition site, in combination with the 5-HT3 receptor antagonists. The potentiation by the GABAA antagonists of [3H]ACh efflux was also observed in a superfusion medium deficient in Cl-. The nonspecific K+-channel blockers TEA and Ba2+ also increased K+-evoked [3H]ACh efflux in this preparation but the releasing effect was not modified by bicuculline. The results support the functional interaction of ondansetron with GABAergic interneurons in the rat entorhinal cortex, GABA-independent mechanisms may however be involved in the regulation of cortical cholinergic function by other 5-HT3 receptor antagonists.

Role of 5-hydroxytryptamine3 (5-HT3) antagonists in the prevention of emesis caused by anticancer therapy

Most anticancer drugs are cytotoxic and produce various side-effects, among which nausea and vomiting are almost ubiquitous and usually extremely distressing to the patient. Cancer chemotherapy elicits two main phases of vomiting: an intense, acute phase of vomiting that occurs almost immediately following anti-cancer therapy and a milder, delayed phase of nausea and vomiting of longer duration. The mechanisms underlying the induction of nausea and vomiting after cancer chemotherapy are poorly understood but may be mediated by serotonin (5-hydroxytryptamine or 5-HT), particularly in the acute phase. Serotonin activates 5-HT3 receptors, which function as ligand-gated ion channels located either in the periphery and/or in the central nervous system to produce emesis, among other effects. The peripheral 5-HT3 receptors may be pharmacologically distinct from the central 5-HT3 receptors and may exhibit some association with GTP-binding proteins. In addition, different populations may exist as distinct subtypes of the same receptor. The 5-HT3 receptor antagonist ondansetron (GR 38032F) is effective in preventing the emesis induced by cytotoxic agents currently used in the treatment of many forms of cancer. Ondansetron has, comparatively, a much higher efficacy in the treatment of acute emesis following cancer chemotherapy than it does in the delayed phase, suggesting that the late phase of emesis may be mediated by other distinct mechanisms.